Cellular communication networks may be configured to enable direct Device-to-Device (D2D) communications, for example, between wireless transmit/receive units (WTRUs) located within radio range of each other. Enabling D2D communications may enhance the spectrum efficiency of a cellular communications network, for example by allowing devices (e.g., WTRUs) to communicate with each other directly rather than sending communications to each other via a corresponding core network. D2D communications may allow devices (e.g., WTRUs) to communicate with each other autonomously even in absence of coverage by a cellular communications network or networks are unavailable due to outage or failure.
However, enabling D2D communications may present resource allocation challenges in a cellular communications network. For example, enabling D2D communications may cause increased interference, such as interference caused by overlapping use (e.g., simultaneous use) of a portion of spectrum for both D2D communications and core network communications. The resource allocation used in a mobile system (e.g., including a base station and one or more WTRUs) may not be suitable for use in D2D communications. D2D communications operating in the absence of cellular communications networks may require management of communications radio resources and operating conditions by devices (e.g., WTRUs) themselves. D2D communications may refer to transmission and/or reception of D2D data.